Most oil and gas wells eventually require some form of stimulation to enhance hydrocarbon flow in order to make or keep them economically viable. The servicing of oil and gas wells to stimulate production requires the pumping of fluids under high-pressure. The fluids are generally corrosive and abrasive because they are frequently laden with corrosive acids and abrasive propants such as sharp sand.
Wellheads are not designed to accommodate delivery of high-pressure, abrasive fluids into the well. Consequently, isolation tools in various forms and configurations have been invented to protect wellheads during well stimulation processes. As knowledge of well stimulation processes have developed, the importance of high delivery rates for successful and economic stimulation processes has been appreciated. Consequently, it is now Applicant's practice to run large bore mandrels through blowout preventers (BOPs) mounted to a well in order to enhance stimulation effects and reduce job time.
Because of the very nature of the stimulation process, most wells to be stimulated have relatively low natural pressure before the stimulation process commences. There are, however, exceptions which may require high-pressure wells to be stimulated for various reasons. In any event, once stimulated, the well may be under very high-pressure. The high-pressure may result from the use of energized stimulation fluids, well known in the art, or natural pressure developed as a result of opening up a high-pressure area of a production zone.
Consequently, situations exist in which the insertion of mandrels used to safely conduct high-pressure fluid through BOPs and other wellhead components or the removal of such mandrels from the wellhead requires mechanical control that cannot be provided by a service rig or a boom truck. For example, a well stimulated with energized fluid may overbear the weight of the mandrel with attached tools and tubing strings. In such situations, the well must be killed before a mandrel can be safely removed. As is well understood in the art, kill fluids are expensive and killing the well may reverse all or part of the beneficial effects of the stimulation process.
Methods and equipment have been devised for inserting these mandrels for protecting wellhead equipment under high-pressures. Examples of these are taught in U.S. Pat. Nos. 4,241,786, 4,867,243 and 6,470,965.
U.S. Pat. No. 4,241,786 issued to Bullen on Dec. 30, 1980, and is entitled WELL TREE SAVER. The apparatus includes a base flange connected to a pair of hydraulic cylinder pistons. Cylinder tops of the hydraulic cylinders are rigidly secured to the mandrel that is supported over top the well, so that motion of the cylinders relative to the pistons induces corresponding motion of the mandrel within the well. As will be evident to those skilled in the art, there is little space available for connecting a single high-pressure stimulation fluid supply line (i.e. a “frac” line) to a high-pressure valve that controls fluid passage through the mandrel, as the cylinders obstruct a substantial portion of a top end of the mandrel, where the high-pressure valve is located. This limited access becomes increasingly problematic when a rig is used parallel with, and proximate the well equipment, as the rig frequently obstructs a substantial part of the mandrel.
U.S. Pat. No. 4,867,243, entitled WELLHEAD ISOLATION TOOL AND SETTING AND METHOD OF USING SAME, which issued to Garner et al. on Sep. 19, 1989, teaches a method of using an apparatus having a single hydraulic cylinder for raising the mandrel from a well under pressure. While meritorious, this apparatus does not permit fluid access to the mandrel. Rather, the mandrel is stroked in, and the apparatus is removed, and then well stimulation equipment is mounted to the mandrel.
U.S. Pat. No. 6,470,965, entitled DEVICE FOR INTRODUCING A HIGH-PRESSURE FLUID INTO WELL HEAD COMPONENTS, issued on Oct. 29, 2002 to Winzer. The device includes two piston cylinders also close to the mandrel, with cylinders that extend above the mandrel top end, and accordingly provide limited access to fracturing lines.
Other devices are known for performing the insertion and removal of a casing mandrel within a well. For example the substitution of the hydraulic cylinders with respective screw jack assemblies is taught in U.S. Pat. No. 4,632,183, entitled INSERTION DRIVE SYSTEM FOR TREE SAVERS, which issued to McLeod on Dec. 30, 1986. The jack assemblies also extend above, and in parallel with, the casing mandrel, obstructing access by the fracturing lines and equipment.
A further problem with current mandrel insertion equipment is that it is a single-purpose device. In general, different equipment is required to lift and land a tubing string, and to perform other like operations (such as a rig or a boom truck, well known in the art). The expense of the single-purpose device makes a higher cost per use of mandrel insertion equipment, and increases the amount and cost of equipment required on-site. Further the alternating use of one lifting/setting device for one function, and then a second lifting/setting device for a next function requires installation and removal of the lifting/setting devices, which adds time and expense to wellhead servicing operations.
Consequently, there exists a need for an apparatus for controlling vertical motion of a tubular within a high-pressure well that provides unobstructed access to a top end of the tubular, and is adapted to permit rotation of the tubular, so that the apparatus can also be used for removing and landing a tubing string, etc.